Is Wall Street ready for the next cyberattack?

Take a deep breath, and imagine a doomsday scenario on Wall Street: a hacktivist group coordinates a large-scale, three-day attack on the capital markets meant to disrupt trading and confidence in the U.S. markets.

That's what cybersecurity firm SIFMA tried to simulate in a Wednesday experiment—where they found that banks might be limited during a hacking by laws that restrict information sharing.

"It's an inevitable instance that we're going to have cyberattacks," said Kenneth Bentsen, SIFMA's CEO said Wednesday on CNBC's "Closing Bell." "We have to work not just on prevention, but on response and recovery. And that's what these exercises are all about."

The third iteration of the experiment, called Quantum Dawn 3, included 80 financial institutions and government entities, such as the Department of the Treasury and FBI. It started with smaller-scale attacks targeted at individual entities through multiple types of systems, followed by a larger attacks that interrupt market operations.

Though the detailed results on how markets did will not be available until October, SIFMA said the exercise highlighted an issue currently being debated in Congress: a Senate bill called the Cybersecurity Information Sharing Act, aimed to clarify the procedure of what information should be kept private and communicated during a corporate data breach.

So far, the bill has awaited passage amid a busy and controversial legislative session.

The previous version of Quantum Dawn, performed in 2013, focused on what executives would do to slow or halt trading during an attempt to shut down the equity markets. The results of that experiment also highlighted coordination efforts in the financial sector, suggesting the industry should strive for greater integration to help decide whether cyber incidents are "systemic," and determining how to communicate with the public if the markets open or close.

Since 2013, resources have poured into better preparing Wall Street for an attack, Bentsen said.

"We know we're going to be hit," Bentsen said. "Now we're working to be prepared for it."